Core idea - two questions:
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What factors (i.e., which particular design decisions) are the most essential to achieving good performance?
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Can we deploy such designs easily?
Key insights
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The most important factor in achieving good performance is using SRPT (or its close cousin, SJF) for packet scheduling. Our results can be summarized in two statements: (1) A rate-setting scheme achieves its best performance when used with SRPT, and (2) with SRPT, a wide range of rate-setting schemes achieve near-optimal performance.
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SRPT is neither necessary nor sufficient for good performance. Clearly, when combined with obviously inappropriate rate-setting schemes (e.g., not increasing the window size sufficiently quickly when flows start, or having extremely long timeout values), the resulting performance with SRPT can be significantly suboptimal; thus, SRPT is not sufficient. In addition, there are several congestion control proposals that mimic SRPT by coordinating host behavior. For instance, pHost approximates SRPT by precisely scheduling packet transmissions from the receivers. Homa adopts the same approach, and additionally, uses a few switch priority queues to improve the approximation accuracy for short flows. With careful tuning, these schemes can perform very well; thus, SRPT at switches is not necessary. However, our point is that with SRPT, near-optimal performance is easy to achieve.
参考文献
Datacenter Congestion Control: Identifying what is essential and making it practical
